(a) Field of the Invention
This invention relates to illuminating systems for endoscopes and more particularly to an illuminating system applicable to an endoscope of a wide angle of view.
(b) Description of the Invention
A conventional illuminating system for endoscopes is formed of an optical system 3 consisting of a light guide 3a and concave lens 3b arranged adjacently to each other in parallel with an observing optical system 2 within a tubular body 1 as shown in FIG. 1. However, as the angle of view of endoscopes has come to increase to be larger than 100 degrees, with such conventional illuminating system as is shown in FIG. 1, it has become difficult to well brightly illuminate the observable range of the endoscope to the peripheral side, because, if the power of the concave lens 3b is increased to brightly illuminate the range to the peripheral side, as shown in FIG. 2, such rays of light as the totally reflecting ray L.sub.1 and the ray L.sub.2 hitting the side of the concave lens 3b will increase and the light amount will be lost. Further, in order to prevent the light from hitting the side of the concave lens, the diameter of the concave lens must be made larger. This is not desirable. In order to eliminate such defects of the conventional illuminating system for endoscopes, as shown in FIG. 3, it is suggested to diagonally cut the exit end face of a light guide 4 and expand the illuminated range by utilizing the refraction of the light on this face. However, in this method, if the angle made by the exit end face 4a of the light guide 4 with the axis 4b of the light guide is made smaller to expand the illuminated range, as shown in FIG. 4, the light will be totally reflected on the exit end face 4a and the light amount loss will be caused. As clear from FIG. 3, it is impossible in principle to expand the range to be illuminated to be larger than 2p. For such reasons, in fact, the illuminating system of such formation as is shown in FIG. 3 can not be used for endoscopes having an angle of view larger than 120 degrees.